This application claims priority from Belgium Application No. 9700581, filed Jul. 7, 1997 and PCT Application No. PCT/BE98/00103, filed Jul. 7, 1998, both of which are hereby incorporated by reference.
This invention concerns a process for the processing of inter-leaved glass and a plant to implement the process.
Interleaved glass is to be understood as a product consisting of two or more sheets of drawn glass, plate glass or cast glass, joined over all their surface by one or a number of intermediate layers not made of glass. These may for example act as wiring that holds together the fragments of glass in case of breakage and ensures residual strength to the whole. Interleaved glass is used in particular in manufacturing the windscreens of vehicles such as motor-cars, aeroplanes, passenger ships, etc., or for safety glass, in particular for bank counters.
Up to now interleaved glass scrap material has been of little or no reuse value. At present, in fact, scrap windscreens are crushed by passing them between two pressure rollers. It might thus be possible to recover certain glass fragments that have separated from the inter-medisate layers and to recycle them, but in general everything is simply dispatched to a dump. The risk, for example, of presence of plastic residues containing fragments of glass makes it inappropriate in current glass recycling operations to recover interleaved glass and recycle it.
The purpose of the present invention is to provide a solution to the problem by simultaneously allowing recovery and perhaps recycling of the material of which the intermediate layers of interleaved glass are made. Advantageously the process and plant set up for this purpose should not lead to another significant environmental problem.
Under the invention the problem posed is resolved by a process of treatment of interleaved glass comprising at least two sheets of glass between which at least one intermediate layer made of a non-glass material is inserted, the said process comprising
fragmentation of the interleaved glass to be processed,
attack of the fragmented interleaved glass with a basic solution,
separation of basic solution, glass and c) non-glass material, this process being characterized by the fact that the attack includes an attack on all the interleaved glass in fragments originating from the fragmentation, in such a way as to obtain an attack medium in which a disassociation takes place, in all the said fragments originating from fragmentation, of non-interleaved fragments of glass and fragments of said non-glass material, that the separation comprises separation between a) the basic solution, b) the fragments of non-interleaved glass that have undergone attack by the basic solution and c) the fragments of non-glass material that have undergone attack by the basic solution, and that the process also includes neutralization of the disassociated fragments b) and c), before any recycling or reuse thereof.
Thus with the process under the invention the glass and the material constituting the intermediate layers are disassociated. The glass and the non-glass material are perfectly clean on leaving the process. They emerge in the form of small fragments immediately reusable in glass processes on one hand, and non-glass materials on the other. This chemical process has the particular feature that it does not involve any chemical reaction between the basic solution and the fragments and that the basic solution remains virtually unaltered after the process, so that it can be reused a number of times for subsequent operations.
The basic attack solution may be water-solution of an OH ion generating agent soluble in water, specifically an alkaline base or earth-alkaline base. preferably NaOH or KOH. Advantageously the basic attack solution is a water-solution of 5 to 15 molar, preferably about 10 molar, NaOH.
Glass may according to the invention be any type of non-composite glass, whether drawn, cast, tinted, transparent, translucent, opaque cut, or treated in another way.
Non-glass material may according to the invention be any material of which the intermediate sheets used in manufacture of interleaved glass are made. Polyvinylbutyral may be mentioned as an example.
According to one mode of implementation of the process according to the invention, the said separation includes sedimentation of a mix of disassociated fragments b) and c), previously separated from the basic solution, in a sedimentation liquid in which the disassociated fragments of the non-interleaved glass having undergone attack by the basic solution b) are deposited, and the disassociated fragments of non-glass material having undergone attack by the basic solution c) float, and a separate collection of the disassociated fragments b) and disassociated fragments c). This mode of implementation advantageously profits from the difference in density between the glass and the non-glass material of the intermediate layers having undergone attack by the basic solution so that they can easily be separated by a simple sedimentation process. The liquid used may advantageously be simply water. Preferably the said liquid does not react in any way either with the fragments of the glass or with the fragments of the non-glass material, and its long use and/or recycling may easily be envisaged.
According to another mode of implementation under the invention, the process comprises the said neutralisation of a mix of the disassociated fragments b) and c), previously separated from the basic solution, by means of an acid not aggressive for glass or the non-glass transparent material. The non-aggressive acid may be a weak acid, in particular phosphoric acid. This acid may also be used on occasion, when the basic attack solution becomes overloaded, to neutralise the basic solution used and thus form a water-solution of sodium phosphate which may itself be reusable, for example in the area of fertiliser manufacture.
This invention also concerns a plant for implementation of the interleaved treatment process. The said plant comprises:
an interleaved glass fragmentation device,
a reactor into which the interleaved glass fragments issuing from the fragmentation device are fed together with a basic solution so as to form an attack medium in which disassociation of all the fragments coming from the fragmentation device into fragments of non-interleaved glass and fragments of the said non-glass material takes place,
a separating device allowing a) the basic solution. b) the disassociated fragments of non-interleaved glass having undergone attack by the basic solution and c) the disassociated fragments of the said non-glass material having undergone attack by the basic solution to be separated, and
a source of neutralising agent enabling neutralisation of the disassociated fragments b) and c) prior to any recycling or reuse.
This relatively simple plant has an entirely justifiable cost as it allows each of the constituent elements of interleaved glass to be reused. A plant of this kind can even be envisaged on one or two semi-trailer platforms in order to provide a mobile plant transportable from dump to dump.
The fragmentation device may be any kind of mill, for example of blade, hammer or ball type, or any crushing device, possibly a mincroniser.